Raman amplifier

Abstract

Raman amplifier includes: a pump-light generator configured to supply pump light to a transmission fiber; a measurement circuit configured to measure a relationship between power of the pump light and power of noise output from the transmission fiber with respect to a range from first pump-light power to second pump-light power; a signal detector configured to monitor a supervisory signal in output light of the transmission optical; and a decision unit configured to decide a state of the transmission fiber according to the monitoring result. When the supervisory signal is detected without the pump light, the measurement circuit measures the relationship while increasing the power of the pump light from the first pump-light power. When the supervisory signal is not detected without the pump light, the measurement circuit measures the relationship while decreasing the power of the pump light from the second pump-light power.

What is claimed is: 
     
       1. A Raman amplifier comprising:
 a pump-light generator configured to supply pump light to a transmission optical fiber; 
 a measurement circuit configured to measure a relationship between power of the pump light and power of noise output from the transmission optical fiber with respect to a range from first pump-light power to second pump-light power that is higher than the first pump-light power; 
 a signal detector configured to monitor a supervisory signal transmitted from a transmission equipment provided at a transmitting end of the transmission optical fiber in output light of the transmission optical fiber; and 
 a decision unit configured to decide a state of the transmission optical fiber according to a monitoring result provided by the signal detector, wherein 
 when the supervisory signal is detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while increasing the power of the pump light from the first pump-light power to the second pump-light power, and 
 when the supervisory signal is not detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while decreasing the power of the pump light from the second pump-light power to the first pump-light power. 
 
     
     
       2. The Raman amplifier according to  claim 1 , wherein
 when the supervisory signal is not detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the decision unit decides the state of the transmission optical fiber according to the monitoring result provided by the signal detector after a specified period of time has elapsed since an instruction to generate pump light with the second pump-light power was given to the pump-light generator. 
 
     
     
       3. The Raman amplifier according to  claim 1 , wherein
 when the supervisory signal is not detected by the signal detector while the measurement circuit measures the relationship, the decision unit decides that the transmission optical fiber has been disconnected. 
 
     
     
       4. The Raman amplifier according to  claim 1 , wherein
 when the supervisory signal is not detected by the signal detector while the measurement circuit measures the relationship, the decision unit shuts down the supply of the pump light from the pump-light generator to the transmission optical fiber. 
 
     
     
       5. The Raman amplifier according to  claim 1 , further comprising
 a power detector configured to detect power of the output light of the transmission optical fiber in a specified wavelength range, wherein 
 the measurement circuit measures the power of the noise using the power detector with respect to a range from the first pump-light power to the second pump-light power, and 
 the supervisory signal is allocated outside the specified wavelength range. 
 
     
     
       6. The Raman amplifier according to  claim 2 , wherein
 the specified period of time is equal to or longer than a period of time required to increase the pump-light power from a level to decide whether or not light having a wavelength of the supervisory signal is present to a level to decide whether or not the supervisory signal is present when the pump-light generator shifts from a state not to generate the pump light to a state to generate the pump light with the second pump-light power. 
 
     
     
       7. The Raman amplifier according to  claim 6 , wherein
 the specified period of time is shorter than a period of time required to stabilize a Raman gain of the transmission optical fiber after an instruction to control the pump-light power has been given to the pump-light generator. 
 
     
     
       8. A Raman amplifier comprising:
 a pump-light generator configured to supply pump light to a transmission optical fiber; 
 a measurement circuit configured to measure a relationship between power of the pump light and power of noise output from the transmission optical fiber with respect to a range from first pump-light power to second pump-light power that is higher than the first pump-light power; 
 a signal detector configured to monitor a synchronization of a frame transmitted from a transmission equipment provided at a transmitting end of the transmission optical fiber in output light of the transmission optical fiber; and 
 a decision unit configured to decide a state of the transmission optical fiber according to a monitoring result provided by the signal detector, wherein 
 when the synchronization of the frame is detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while increasing the power of the pump light from the first pump-light power to the second pump-light power, and 
 when the synchronization of the frame is not detected by the signal detector while the pump light is not supplied to the transmission optical fiber, the measurement circuit measures the relationship while decreasing the power of the pump light from the second pump-light power to the first pump-light power.